This invention relates to the incorporation of oxides of lead and tin to modify the ballistic properties of high energy double-base propellants containing energetic nitramine crystalline filler.
One of the most desired characteristics of a ballistic rocket employing a propellant is reliability of performance. This reliability of performance is dependent upon many factors one of which is propellant ballistic properties. In this respect a propellant whose burning rate is invarient or nearly invarient to changes in temperature and pressure would be most ideal for an end item application. The variation of propellant burning rate at a given temperature to changes in pressure is expressed as pressure exponent n which is the slope of the burning rate isotherm between two pressure levels obtained from a log plot of burning rate data. As the value of n is lowered the burning rate of the propellant becomes more stable to changes in pressure.
The interdependence of propellant burning rate and pressure to change in temperature is expressed as the temperature coefficient (.pi..sub.p/r. %/.degree. F) which is the percent change in pressure exhibited by a propellant per degree change in temperature at a constant p/r ratio. The lower the temperature coefficient, the less dependent the burning rate of the propellant is to pressure-temperature changes. Generally, propellants, especially high energy systems are usually capable of exhibiting either favorable pressure exponents or temperature coefficients but systems exhibiting both of these qualities are considered unique.
Combustion catalysts, in the form of organo-metallic and inorganic salts have been employed as ballistic modifiers to obtain the above ballistic effects in double base propellants of low, intermediate, and high energy for a considerable period of time. However, most efficient ballistic modification (stability of burning rate to variations in temperature and pressure) has been realized with double base systems of low to intermediate energy (Q, heat of explosion approximately 640 to 950 cal./gr.), which do not contain explosive crystalline filler, and double base systems of low energy (Q, heat of explosion approximately 600 to 800 cal./gr.) which contain nitramine (cyclotrimethylenetrinitramine, cyclotetramethylene tetra nitramine, etc.) energetic crystalline fillers. All efforts to modify the ballistics of high energy extruded and pourable propellants (Q, heat of explosion 950 cal./gr. and above) containing crystalline nitramines with organo-metallic and inorganic salts have produced systems with only minimal ballistic properties.
It is therefore an object of this invention to provide improved ballistic modification to a high energy nitramine double base propellant.
A further object of this invention is to provide a method of incorporation of the ballistic modifier into the high energy nitramine double base propellant.
Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the following detailed description.
According to this invention improved ballistic modification is obtained by incorporation of a mixture of lead and tin oxides into a nitramine double base propellant.